A device is described for example in German Patent Application No. DE 101 35 142, and is used for example in the intake section of an internal combustion engine to determine the air mass flow that is supplied to the internal combustion engine through a conduit. A segment, provided with a bypass part, of a sensor device is placed into the conduit part through a plug-in opening. The bypass part has a channel structure having an inlet area from which a measurement channel branches off that is provided with the measurement element. The inlet area additionally has a separation zone having at least one separation opening that opens into the conduit passageway at at least one side wall of the bypass part. The separation zone is used to separate out liquid and/or solid particles from the channel structure, so that they are prevented from entering the measurement channel provided with the measurement element and contaminating the measurement element.
In the known devices, the edges formed by the front side, facing the main flow direction, and the side walls of the bypass part placed into the conduit form leading edges, in whose areas separated flows arise, which on the one hand can cause large pressure losses and on the other hand can cause an unintended pulsation in the flow, as a result of which pressure fluctuations are transmitted through the separation opening to the measurement channel that branches off from the inlet area. The pressure fluctuations in the measurement channel can significantly falsify the output signal of the measurement element.